In a conventionally known method for manufacturing a tire, a base tire, which is the base of a tire, and an annular tread, which serves as the tread of the tire, are built separately. Then the tread is mounted on the base tire by a tire manufacturing apparatus.
For example, such a tire manufacturing apparatus is comprised of a base tire holding unit for holding a base tire, a tread holding unit for expandably and contractably holding a tread, a moving means for moving the tread holding unit toward and back from the base tire holding unit, and a pressing means for pressing the tread onto the outer periphery of the base tire when fitting the tread on the base tire.
On the above-mentioned tire manufacturing apparatus, abase tire, with air filled in it, is secured rotatably to the drum of the apparatus. Also, its tread holding unit has an expansion/contraction mechanism capable of synchronously expanding radially a plurality of annularly arranged bar members, each bar member having a plurality of rollers in the extension direction. And the tread is held with its inner periphery riding the bar members of the expansion mechanism. Then the tread is radially expanded wider than the outside diameter of the base tire as the bar members holding the tread are moved radially outward. And the tread, together with the tread holding unit, is moved to a position where the inner periphery of the tread is in a predetermined position relative to the outer periphery of the base tire. When the tread is located in the predetermined position relative to the base tire, the bar members are moved radially inward until they come into contact with the outer periphery of the base tire. Then as the tread is pressed to the base tire, with the pressing means of the tread holding unit pressing the outer periphery of the tread, the plurality of bar members are pulled out from between the tread and the base tire. Thus the tread and the base tire are fitted together into a single body.
However, the above-described tire manufacturing apparatus is of such structure that the tread is held and spread radially wider by a plurality of bar members. Hence, there result differences in expansion between the parts of the tread where they are held by the bar members and the other parts thereof where they are not. It is therefore possible that the diameter of the tread is not expanded uniformly along the circumference.
Also, when the tread is mounted on the base tire, the bar members are pulled out as the tread is pressed to the base tire with the pressing means. Therefore, it is possible that the areas of the tread other than the parts where they are pressed by the pressing means are fitted on the base tire with some deviation (position gap) in the axial direction of the tire. This may hamper the improvement of productivity by manufacturing quality tires efficiently.